Looking at the specs on the 't' vs 'tR' for the Note 3 (on their
Amazon product page), they specify that the 'tR' is 0.4 mm, and that the 't' is 0.26mm - and referenced as being 35% slimmer. Well.... 0.4mm less 35% leaves 0.26mm.
Fast forward to the same respective models for the Nexus 5. The 'tR' doesn't indicate thickness, but the 't' is only 0.26mm and listed as "35% slimmer and lighter than the previous model." Short of direct confirmation to the contrary, I think it's reasonable to presume that the 'tR' model is 0.4mm thick (which makes sense to a degree - if you're going to be able to roll the edges without their becoming
too thin at a point, you may need to start with a slightly thicker slab).
So 't' looks to be the best option if you plan on using a case (thinner, lighter glass, inappropriate w/o a case as the exposed edges are more susceptible to chipping; while the 'tR' is best without a case.
That being said, it looks like they have a new series of '
NANO.SLIM" they introduced for the GS4 and iPhones (but not (yet?) for Nexus), running as thin as 0.15mm. While it would be the most stealth install, and should cover against scratches as well, I suspect it wouldn't do as well vs. impact - depends on what you're looking for.